Influence of immunosuppressive drugs on dendritic cells

Anti-Inflammatory Effect of Fermented Cabbage Extract Containing Nitric Oxide Metabolites with Silica

The aim of this study was to evaluate the anti-inflammatory effect of fermented cabbage extract (FC) containing nitric oxide metabolites with silica (FCS) on 1-fluoro-2,4-dinitrofluorobenzene (DNFB)-induced atopic dermatitis (AD) in BALB/c mice. Atopic dermatitis-like allergic contact dermatitis was induced by DNFB challenge in the ear after DNFB sensitization on the dorsal skin of mice. FCS alleviated the severity of atopic dermatitis-like skin lesions. In addition, epidermis thickness of the ear and penetration of inflammatory cells in atopic dermatitis-like skin lesions were decreased after topical application of FCS. The serum levels of TNF-α and IL-4 were measured in atopic dermatitis mice using ELISA kits, which were observed to be significantly decreased after topical application of FCS. This study demonstrates that the FCS can be used as a potential therapeutic for the treatment and prevention of AD.

Immunosuppressive effect of Columbianadin on maturation, migration, allogenic T cell stimulation and phagocytosis capacity of TNF-α induced dendritic cells

ETHNOPHARMACOLOGICAL RELEVANCE

Angelicae pubescentis radix (APR) has a long history in the treatment of rheumatoid arthritis (RA) in China. It has the effects of dispelling wind to eliminate dampness, removing arthralgia and stopping pain in the Chinese Pharmacopeia, but its mechanisms was unclear. Columbianadin (CBN) was one of the main bioactive compounds of APR, and has many pharmacological effects. But the immunosuppressive effect of CBN on DCs and the potential mechanism needed to be explored.

AIM OF THE STUDY

The study was aimed to clarify the immunosuppressive effect of CBN on maturation, migration, allogenic T cell stimulation and phagocytosis capacity of TNF-α induced DCs.

MATERIALS AND METHODS

Bone marrow-derived DCs were obtained and cultured from C57BL/6 mice in accordance with protocol. The phenotypic study (CD11c, CD40, CD80, CD86 and MHC Ⅱ) were measured by flow cytometry. FITC-dextran were uptaked by DCs and the change of endocytosis activity were mediated by acquired mannose receptor. Transwell chambers were used to detect the migration ability of DCs. Mixed leukocyte reaction (MLR) assay was used to detect the allostimulatory ability of CBN on TNF-α stimulated DCs. The secretion of cytokines and chemokines was measured by ELISA Kit. TLRs gene and MAPKs/NF-κB protein expression were checked by qRT-PCR and Western blot.

RESULTS

CBN inhibited the maturation of TNF-α-induced DCs while maintaining phagocytosis capabilities. Additionally, CBN inhibited the migration of TNF-α stimulated DCs, which related to reduce the production of chemokines (MCP-1, MIP-1α). Notably, CBN could suppress the proliferation of CD4⁺T cells by inhibiting DCs maturation, and decrease the proinflammatory cytokines IL-6 production. Furthermore, CBN inhibited mRNA expression of TLR2, TLR7 and TLR9 in TNF-α-activated DCs. Meanwhile, the phosphorylation of p38, JNK1/2 and NF-κB protein were significantly inhibited in CBN treated DCs.

CONCLUSIONS

These findings provided novel insights into the pharmacological activity of CBN. They also indicated that inhibition DCs maturation owning to the immunosuppressive effect of CBN. CBN was expected as a potential immunosuppressant and TLRs/MAPKs/NF-κB pathway may be an important mechanism for CBN's immunosuppressive activity.

A rare case of salmonellosis with multifocal osteomyelitis and pulmonary involvement

Salmonellosis is characterized by gastroenteritis and enteric fever in humans and affects various organs, particularly in endemic regions and in immunocompromised patients. Here, we report on a 45-year-old male patient with multifocal osteomyelitis, pneumonia and colonic ulcers caused by Salmonella typhi infection. The patient was admitted to our outpatient department with dysuria, fever and hip pain and had been treated with prednisolone and methotrexate for pemphigus vulgaris for two months. After Salmonella typhi was isolated in the urine culture, the patient was hospitalized and treated according to the antibiogram. However, despite antibiotherapy, the patient's ongoing complaints suggested an existing resistance problem or a rare or atypical involvement of Salmonella spp. As immunosuppressive agents were not used in high doses or for prolonged periods, this disease course and severity were not expected. For an infectious process with an atypical course or multiorgan involvement, particularly in endemic regions and immunocompromised patients, salmonellosis should be considered in the differential diagnosis.

Frequency of dendritic cell subsets and ILT3, ILT4 gene expression in two different immunosuppressive protocols in kidney transplant recipients. A cohort report

Dendritic cells (DCs) have a major role in the initiation of an immune response and Immunoglobulin-like transcript 3&4 (ILT3&ILT4) are inhibitory receptors that induce tolerance in DCs. Recent studies show that immunosuppressive agents affect frequency of DCs. Herein, we compared the effect of mycophenolate mofetil (MMF) and sirolimus (SRL) in tacrolimus (TAC)-based immunosuppression on DC subsets frequency and ILT3/ILT4 gene expression in kidney transplant recipients. We enrolled 24 adult transplant recipients who received MMF/TAC (n = 14) or SRL/TAC (n = 10). Peripheral blood samples were obtained from recipients, 24-48 h before transplantation and 4 months after transplantation. The frequency of DC subsets was analyzed by flow cytometry and gene expression of ILT3/ILT4 were estimated by real-time PCR. Our results showed that MMF vs. SRL treated recipient showed an increase in pDC % with increased in the expression of ILT3/ILT4 which is in favor of better allograft survival; However, for confirming the results of this preliminary study, a cohort study with larger sample size is necessary.

Dendritic Cells and Their Role in Cardiovascular Diseases: A View on Human Studies

The antigen-presenting dendritic cells (DCs) are key to the immunological response, with different functions ascribed ranging from cellular immune activation to induction of tolerance. Such immunological responses are involved in the pathophysiological mechanisms of cardiovascular diseases, with DCs shown to play a role in atherosclerosis, hypertension, and heart failure and most notably following heart transplantation. A better understanding of the interplay between the immune system and cardiovascular diseases will therefore be critical for developing novel therapeutic treatments as well as innovative monitoring tools for disease progression. As such, the present review will provide an overview of DCs involvement in the pathophysiology of cardiovascular diseases and how targeting these cells may have beneficial effects for the prognosis of patients.

Role of Dendritic Cells in the Induction of Lymphocyte Tolerance

The ability of dendritic cells (DCs) to trigger tolerance or immunity is dictated by the context in which an antigen is encountered. A large body of evidence indicates that antigen presentation by steady-state DCs induces peripheral tolerance through mechanisms such as the secretion of soluble factors, the clonal deletion of autoreactive T cells, and feedback control of regulatory T cells. Moreover, recent understandings on the function of DC lineages and the advent of murine models of DC depletion have highlighted the contribution of DCs to lymphocyte tolerance. Importantly, these findings are now being applied to human research in the contexts of autoimmune diseases, allergies, and transplant rejection. Indeed, DC-based immunotherapy research has made important progress in the area of human health, particularly in regards to cancer. A better understanding of several DC-related aspects including the features of DC lineages, milieu composition, specific expression of surface molecules, the control of signaling responses, and the identification of competent stimuli able to trigger and sustain a tolerogenic outcome will contribute to the success of DC-based immunotherapy in the area of lymphocyte tolerance. This review will discuss the latest advances in the biology of DC subtypes related to the induction of regulatory T cells, in addition to presenting current ex vivo protocols for tolerogenic DC production. Particular attention will be given to the molecules and signals relevant for achieving an adequate tolerogenic response for the treatment of human pathologies.

Rapid reconstitution of functionally active 6-sulfoLacNAc(+) dendritic cells (slanDCs) of donor origin following allogeneic haematopoietic stem cell transplant

The role of dendritic cells (DCs) and macrophages in allogeneic haematopoietic stem cell transplant (HSCT) is critical in determining the extent of graft-versus-host response. The goal of this study was to analyse slanDCs, a subset of human proinflammatory DCs, in haematopoietic stem cell (HSC) sources, as well as to evaluate their 1-year kinetics of reconstitution, origin and functional capacities in peripheral blood (PB) and bone marrow (BM) of patients who have undergone HSCT, and their presence in graft-versus-host disease (GVHD) tissue specimens. slanDCs were also compared to myeloid (m)DCs, plasmacytoid (p)DCs and monocytes in HSC sources and in patients' PB and BM throughout reconstitution. slanDCs accounted for all HSC sources. In patients' PB and BM, slanDCs were identified from day +21, showing median frequencies comparable to healthy donors, donor origin and kinetics of recovery similar to mDCs, pDCs, and monocytes. Under cyclosporin treatment, slanDCs displayed a normal pattern of maturation, and maintained an efficient chemotactic activity and capacity of releasing tumour necrosis factor (TNF)-α upon lipopolysaccharide (LPS) stimulation. None the less, they were almost undetectable in GVHD tissue specimens, being present only in intestinal acute GVHD samples. slanDCs reconstitute early, being donor-derived and functionally competent. The absence of slanDCs from most of the GVHD-targeted tissue specimens seems to rule out the direct participation of these cells in the majority of the local reactions characterizing GVHD.

Role of dendritic cells in the context of acute cellular rejection: comparison between tacrolimus- or cyclosporine A-treated heart transplanted recipients

BACKGROUND

In the last years many studies have been designed to predict risk of acute rejection and to adapt the immunosuppressive therapy. The importance of dendritic cells (DCs) in the immune response, especially their role in tolerance is known. Thus, we investigated the influence of tacrolimus (TAC)-based and of cyclosporine A (CsA)-based immunosuppressive therapies on dendritic cells and the incidence of rejection in heart transplant recipients.

METHODS

Groups consisted of 14 CsA treated and 15 TAC treated patients. At different study time points (0, 3 and 6 months after study begin) peripheral blood from the patients was drawn to analyse (1) blood concentration of CsA or TAC (trough value) and (2) percentages of plasmacytoid and myeloid DC (p and mDC) subsets using flow cytometry. Histological rejection grading was performed of endomyocardial biopsies.

RESULTS

TAC treated patients had significantly higher values of pDCs (CsA group 53.9%±13.0%; TAC group 67.5%±8.4%; p<0.05) and significantly lower values of mDCs than CsA treated patients (CsA group 58%±19.0%; TAC group 45.2%±10.7%; p<0.05). In general, HTx patients with rejection grade of ≥2 had significant lower values of pDCs (55.1%±16.2%) compared to patients without rejection (63.6%±10.5%; p<0.05). TAC-treated patients had significantly less rejections CsA-treated patients (CsA group 0.86±0.95; TAC group 0.2±0.4; p<0.05).

CONCLUSIONS

Our results showed that HTx patients with high pDCs had a lower risk for rejection and that TAC-treated patients had higher pDCs values compared to CsA-treated patients. Future studies need to define individual pDC values to predict acute cellular rejection.

Regulatory myeloid cells in transplantation

Regulatory myeloid cells (RMC) are emerging as novel targets for immunosuppressive (IS) agents and hold considerable promise as cellular therapeutic agents. Herein, we discuss the ability of regulatory macrophages, regulatory dendritic cells, and myeloid-derived suppressor cells to regulate alloimmunity, their potential as cellular therapeutic agents, and the IS agents that target their function. We consider protocols for the generation of RMC and the selection of donor- or recipient-derived cells for adoptive cell therapy. Additionally, the issues of cell trafficking and antigen (Ag) specificity after RMC transfer are discussed. Improved understanding of the immunobiology of these cells has increased the possibility of moving RMC into the clinic to reduce the burden of current IS agents and to promote Ag-specific tolerance. In the second half of this review, we discuss the influence of established and experimental IS agents on myeloid cell populations. IS agents believed historically to act primarily on T cell activation and proliferation are emerging as important regulators of RMC function. Better insights into the influence of IS agents on RMC will enhance our ability to develop cell therapy protocols to promote the function of these cells. Moreover, novel IS agents may be designed to target RMC in situ to promote Ag-specific immune regulation in transplantation and to usher in a new era of immune modulation exploiting cells of myeloid origin.

Stressful presentations: mild cold stress in laboratory mice influences phenotype of dendritic cells in naïve and tumor-bearing mice

The ability of dendritic cells (DCs) to stimulate and regulate T cells is critical to effective anti-tumor immunity. Therefore, it is important to fully recognize any inherent factors which may influence DC function under experimental conditions, especially in laboratory mice since they are used so heavily to model immune responses. The goals of this report are to 1) briefly summarize previous work revealing how DCs respond to various forms of physiological stress and 2) to present new data highlighting the potential for chronic mild cold stress inherent to mice housed at the required standard ambient temperatures to influence baseline DCs properties in naïve and tumor-bearing mice. As recent data from our group shows that CD8⁺ T cell function is significantly altered by chronic mild cold stress and since DC function is crucial for CD8⁺ T cell activation, we wondered whether housing temperature may also be influencing DC function. Here we report that there are several significant phenotypical and functional differences among DC subsets in naïve and tumor-bearing mice housed at either standard housing temperature or at a thermoneutral ambient temperature, which significantly reduces the extent of cold stress. The new data presented here strongly suggests that, by itself, the housing temperature of mice can affect fundamental properties and functions of DCs. Therefore differences in basal levels of stress due to housing should be taken into consideration when interpreting experiments designed to evaluate the impact of additional variables, including other stressors on DC function.

Tolerogenic dendritic cells derived from donors with natural rubber latex allergy modulate allergen-specific T-cell responses and IgE production

Natural rubber latex (NRL; Hevea brasiliensis) allergy is an IgE-mediated reaction to latex proteins. When latex glove exposure is the main sensitizing agent, Hev b 5 is one of the major allergens. Dendritic cells (DC), the main antigen presenting cells, modulated with pharmacological agents can restore tolerance in several experimental models, including allergy. In the current study, we aimed to generate DC with tolerogenic properties from NRL-allergic patients and evaluate their ability to modulate allergen-specific T and B cell responses. Here we show that dexamethasone-treated DC (dxDC) differentiated into a subset of DC, characterized by low expression of MHC class II, CD40, CD80, CD86 and CD83 molecules. Compared with LPS-matured DC, dxDC secreted lower IL-12 and higher IL-10 after CD40L activation, and induced lower alloantigenic T cell proliferation. We also show that dxDC pulsed with the dominant Hev b 5 T-cell epitope peptide, Hev b 5_46–65^, inhibited both proliferation of Hev b 5-specific T-cell lines and the production of Hev b 5-specific IgE. Additionally, dxDC induced a subpopulation of IL-10-producing regulatory T cells that suppressed proliferation of Hev b 5-primed T cells. In conclusion, dxDC generated from NRL-allergic patients can modulate allergen-specific T-cell responses and IgE production, supporting their potential use in allergen-specific immunotherapy.

Phenotypic and functional maturation of murine dendritic cells induced by 18 alpha- and beta-glycyrrhetinic acid

Various studies have described glycyrrhizin (GL), an active triterpenoic saponin extract of licorice roots, as an anti-inflammatory, antiviral, antimicrobial, anti-tumor and immunomodulating agent. The activity of GL has been mainly attributed to its metabolites, 18-alpha (GA) and 18-beta-glycyrrhetinic acid (GB), which their mechanism of action on the immune system cells is not clearly known. In this study, we have investigated the effects of GA and GB on the immune system by targeting dendritic cells and analyzing phenotypic and functional maturity of murine dendritic cells (DCs) after treatment with these components. Stimulation of DCs with GA and GB resulted in up-regulation of CD40, CD86 and MHC-II molecules indicating their effects on the maturation of DCs. These components induced the allogenic immunostimulatory capacity of DCs by stimulating the proliferation of T cells and production of the T helper (h)1-promoting cytokine, IL-12. They also increased the production of IFN-γ by T cells in mixed-lymphocyte reaction. In conclusion, these results indicate that GA and GB may insert their immunomodulatory effects by enhancing DC maturation and modulating Th1/Th2 response through an increase in Th1 responses, implying their beneficial in host defense against infectious diseases.

Dendritic cell therapy for Type 1 diabetes suppression

While dendritic cell-based therapy is a clinical reality for human malignancies, until now, some conceptual concerns have served to delay its consideration to treat human autoimmune diseases, even in light of almost two decades' worth of overwhelmingly supportive preclinical animal studies. This article provides an overview of the development of dendritic cell-based therapy for Type 1 diabetes mellitus, given that this is the best-studied autoimmune disorder and that there is a good understanding of the underlying immunology. This article also highlights data from the authors' pioneering Phase I clinical trial with tolerogenic dendritic cells, which hopes to motivate the clinical translation of other dendritic cell-based approaches, to one or more carefully selected Type 1 diabetic patient populations.

Chimerism-based experimental models for tolerance induction in vascularized composite allografts: Cleveland clinic research experience

The preclinical experimental models of vascularized composite allografts (VCAs) have been rapidly developed for the assessment of immunomodulatory protocols for clinical application. Recently, researchers have focused on immunomodulatory protocols which overcome the immunologic barrier between the allogeneic donor and recipient and may lead to tolerance induction. In order to test the feasibility of chimerism induction, experimental VCAs have been performed in different models including rodents, large animals, and nonhuman primates. These models differ in the complexity of transplanted tissue and in their responses to immunomodulatory protocols. In most applications, VCA contains multiple-tissue components; however, each individual component of CTA possesses unique immunologic characteristics that ultimately contribute to the chimerism induction and successful outcome of the VCA. Heterogenic character and complexity of tissue components in different VCA models determine the quality and robustness of donor-specific chimerism. As introduced in experimental studies, variable immunomodulatory options have been studied to achieve tolerance to VCA in rodents and large animal models allowing for widespread application in clinic. In this paper, based on our own experience, we have analyzed the current knowledge of tolerance-inducing strategies via chimerism induction in VCA experimental models in the context of immunomodulatory protocols and VCA complexity and their relevance and applicability to clinical practice.

Dexamethasone counteracts the immunostimulatory effects of triiodothyronine (T3) on dendritic cells

Glucocorticoids (GCs) are widely used as anti-inflammatory and immunosuppressive agents. Several studies have indicated the important role of dendritic cells (DCs), highly specialized antigen-presenting and immunomodulatory cells, in GC-mediated suppression of adaptive immune responses. Recently, we demonstrated that triiodothyronine (T3) has potent immunostimulatory effects on bone marrow-derived mouse DCs through a mechanism involving T3 binding to cytosolic thyroid hormone receptor (TR) β1, rapid and sustained Akt activation and IL-12 production. Here we explored the impact of GCs on T3-mediated DC maturation and function and the intracellular events underlying these effects. Dexamethasone (Dex), a synthetic GC, potently inhibited T3-induced stimulation of DCs by preventing the augmented expression of maturation markers and the enhanced IL-12 secretion through mechanisms involving the GC receptor. These effects were accompanied by increased IL-10 levels following exposure of T3-conditioned DCs to Dex. Accordingly, Dex inhibited the immunostimulatory capacity of T3-matured DCs on naive T-cell proliferation and IFN-γ production while increased IL-10 synthesis by allogeneic T cell cultures. A mechanistic analysis revealed the ability of Dex to dampen T3 responses through modulation of Akt phosphorylation and cytoplasmic-nuclear shuttling of nuclear factor-κB (NF-κB). In addition, Dex decreased TRβ1 expression in both immature and T3-maturated DCs through mechanisms involving the GC receptor. Thus GCs, which are increased during the resolution of inflammatory responses, counteract the immunostimulatory effects of T3 on DCs and their ability to polarize adaptive immune responses toward a T helper (Th)-1-type through mechanisms involving, at least in part, NF-κB- and TRβ1-dependent pathways. Our data provide an alternative mechanism for the anti-inflammatory effects of GCs with critical implications in immunopathology at the cross-roads of the immune-endocrine circuits.

Mycobacterium ulcerans triggers T-cell immunity followed by local and regional but not systemic immunosuppression

Buruli ulcer is a neglected infectious disease caused by Mycobacterium ulcerans and is characterized by necrotic cutaneous lesions induced by the exotoxin mycolactone. Despite evidence of Th1-mediated protective immunity, M. ulcerans infection has been associated with systemic immunosuppression. We show that early during mouse infection with either mycolactone-positive or negative strains, pathogen-specific gamma interferon (IFN-γ)-producing T cells developed in the draining lymph node (DLN). CD4(+) cells migrated to the infection foci, but progressive infection with virulent M. ulcerans led to the local depletion of recruited cells. Moreover, dissemination of virulent M. ulcerans to the DLN was accompanied by extensive DLN apoptotic cytopathology, leading to depletion of CD4(+) T cells and abrogation of IFN-γ expression. Advanced footpad infection with virulent M. ulcerans did not induce increased susceptibility to systemic coinfection by Listeria monocytogenes. These results show that infection with M. ulcerans efficiently triggers a mycobacterium-specific T-cell response in the DLN and that progression of infection with highly virulent M. ulcerans leads to a local and regional suppression of that immune response, but without induction of systemic immunosuppression. These results suggest that prophylactic and/or therapeutic interventions to prevent dissemination of M. ulcerans to DLN during the early phase of infection would contribute for the maintenance of protective immunity and disease control.

Dendritic cells and regulation of alloimmune responses: relevance to outcome and therapy of organ transplantation

Dendritic cells are uniquely well-equipped for antigen capture, processing and presentation. They are highly-efficient antigen-presenting cells that induce and regulate T-cell reactivity. Due to their inherent tolerogenicity, immature dendritic cells offer considerable potential as candidate cellular vaccines for negative regulation of immune reactivity/promotion of tolerance. Both classic myeloid and, more recently, characterized plasmacytoid dendritic cells, exhibit tolerogenic properties. Manipulation of dendritic cells differentiation/ maturation in the laboratory using cytokines, pharmacologic agents or genetic engineering approaches can render stably immature dendritic cells that promote organ transplant tolerance in rodents. There are also indications from human studies of the ability of dendritic cells to promote T-cell tolerance and induce T-regulatory cells, with potential for therapeutic application in organ transplantation. In addition, recent clinical observations suggest that modulation of dendritic cell function (e.g., by immunosuppressive drugs) affects the outcome of transplantation. The challenge confronting applied dendritic cell biology is the identification of optimal strategies and therapeutic regimens to allow the potential of these powerful immune regulatory cells to be realized in the clinic.

Biomaterial adjuvant effect is attenuated by anti-inflammatory drug delivery or material selection

Biomaterials have been shown to differentially support dendritic cell (DC) maturation, a prerequisite for an adjuvant effect. Treatment of DCs with poly(D,L-lactic-co-glycolic acid) (PLGA) films resulted in DC maturation but agarose films did not. In these studies, the biomaterial adjuvant effect was attenuated by material selection (PLGA or agarose scaffolds) or local delivery of an anti-inflammatory/immunosuppressive glucocorticoid, dexamethasone (DX), from PLGA scaffolds. Porous scaffolds (SCs) of PLGA or agarose were produced to deliver equivalent amounts of model antigen, ovalbumin (OVA). Alternatively, PLGA SCs with incorporated OVA were produced with or without DX. These SCs were implanted individually, subcutaneously, and dorsally in C57BL/6 mice. Blood was collected from mice at specific times over a 12-week duration for measurement of antibody production against OVA. Scaffolds were explanted at 12 weeks for histological examination of foreign body response. Scaffolds of PLGA, but not of agarose, were found to elicit higher antibody production against co-delivered OVA, than negative controls. Short-term delivery of DX from PLGA SCs delivering OVA temporarily delayed onset of anti-OVA antibody production. More sustained release of DX at an effective dose and with an appropriate time course is expected to extend the effect of DX on the biomaterial adjuvant effect. The immunomodulatory ability of biomaterials to affect the immune response to co-delivered antigen is demonstrated wherein this immunomodulatory ability correlates with the observed in vitro differential effects of biomaterials on DC maturation.

FK506 as an adjuvant of tolerogenic DNA vaccination for the prevention of experimental autoimmune encephalomyelitis

BACKGROUND

DNA vaccination is a strategy that has been developed primarily to elicit protective immunity against infection and cancer.

METHODS

DNA vaccine was used, in conjunction with an immunosuppressant, to tolerize harmful autoimmunity.

RESULTS

Immunization of C57BL/6 mice with MOG(35-55), a myelin oligodendrocyte glycoprotein-derived peptide, and FK506 (Tacrolimus) as a tolerogenic adjuvant stimulated regulatory dendritic cells, induced antigen-specific regulatory T cells (Treg), and protected the animals from subsequent induction of experimental autoimmune encephalomyelitis (EAE). After EAE induction, there were fewer lymphocytes, including fewer T helper 17 cells, and more Treg infiltrating the spinal cord in the immunized mice compared to in control mice. Furthermore, at the peak of the EAE manifestation, CD4 T cells in the immunized mice showed decreased expression of interferon-gamma and interleukin (IL)-17, but not IL-4, in treated mice.

CONCLUSIONS

DNA vaccination, when applied with an immunosuppressant as adjuvant, can induce antigen-specific tolerance and prevent autoimmune disease.

Long-Term Laryngeal Allograft Survival Using Low-Dose Everolimus

OBJECTIVE: The purpose of this study was to explore the mechanism and utility of everolimus as a single-agent therapy in preventing mouse laryngeal allograft rejection.

STUDY DESIGN: Prospective animal study.

SETTING: Academic research at a tertiary medical center.

SUBJECTS AND METHODS: Fifteen recipient mice (five per group) were injected with everolimus (1 mg/kg/d) until euthanized at 15, 30, and 60 days posttransplantation. Five mice received transplants without immunosuppression and were euthanized at day 15. Larynges were graded for rejection severity. Draining lymph nodes and spleens were evaluated by flow cytometry to assess the systemic immunological environment.

RESULTS: Each time group demonstrated minor allograft rejection (rejection severity scores: 2.51, 2.46, 2.78; no rejection, 1; severe, 6). This was not significantly different between groups. Everolimus-treated mice had significantly less rejection at all time points compared with non-immunosuppressed mice. Flow cytometry showed a blunted cytotoxic T-cell response, differentiation favoring regulatory T-cells, and decreased number and function of dendritic cells.

CONCLUSIONS: Everolimus successfully prevents laryngeal allograft rejection up to 60 days posttransplantation. It appears to increase the production of regulatory T-cells while decreasing cytotoxic T-cell and dendritic cell response. Everolimus alone or in combination with other immunosuppressants may enable laryngeal transplantation to become a viable reconstructive option following laryngectomy for malignancy.

Prednisolone treatment induces tolerogenic dendritic cells and a regulatory milieu in myasthenia gravis patients

FOXP3-expressing naturally occurring CD4(+)CD25(high) T regulatory cells (Treg) are relevant in the control of autoimmunity, and a defect in this cell population has been observed in several human autoimmune diseases. We hypothesized that altered functions of peripheral Treg cells might play a role in the immunopathogenesis of myasthenia gravis, a T cell-dependent autoimmune disease characterized by the presence of pathogenic autoantibodies specific for the nicotinic acetylcholine receptor. We report in this study a significant decrease in the in vitro suppressive function of peripheral Treg cells isolated from myasthenia patients in comparison to those from healthy donors. Interestingly, Treg cells from prednisolone-treated myasthenia gravis patients showed an improved suppressive function compared with untreated patients, suggesting that prednisolone may play a role in the control of the peripheral regulatory network. Indeed, prednisolone treatment prevents LPS-induced maturation of monocyte-derived dendritic cells by hampering the up-regulation of costimulatory molecules and by limiting secretion of IL-12 and IL-23, and enhancing IL-10. In addition, CD4(+) T cells cultured in the presence of such tolerogenic dendritic cells are hyporesponsive and can suppress autologous CD4(+) T cell proliferation. The results shown in this study indicate that prednisolone treatment promotes an environment that favors immune regulation rather than inflammation.

Dendritic cells and chemokine-directed migration in transplantation: where are we headed?

The role of dendritic cells (DC) in transplantation is often overshadowed by the more prominent roles of T and B cells, which interact directly with and, in the absence of immunosuppressive therapy, destroy the allograft. It has become increasingly recognized, however, that these potent antigen-presenting cells exert control over the immune response and regulate the balance between tolerance and immunity to transplanted organs and tissues. The role that chemokines play in influencing DC function with impact on regulation of immune responses against the graft is only beginning to be understood. This article considers how the manipulation of DC trafficking during an alloimmune response can affect graft outcome.

Immunoregulatory profiles in liver transplant recipients on different immunosuppressive agents

We compared peripheral blood immunophenotyping in 31 adult liver transplant recipients on differing long-term immunosuppressive (IS) monotherapy with and without peri-transplantation alemtuzumab (AL) induction. All patients had been stable on monotherapy with either sirolimus (SRL) (n = 10) or without SRL (tacrolimus (TAC) (n = 10), mycophenolate mofetil (MMF) (n = 11)) for more than 6 months. Five-color flow cytometry for putative "regulatory" T and dendritic cells as well as serum assays for soluble HLA-G (sHLA-G) were performed. The SRL monotherapy group had significantly higher percentages of CD4+CD25(high+)Foxp3+ T cells (1.3 +/- 1.0) compared with the non-SRL group (0.7 +/- 0.6) (p = 0.04). The SRL effect was even higher in a subset with prior AL induction and no prior hepatitis C or rejection (1.7 +/- 0.2) compared with all other subgroups (0.7 +/- 0.6) (p = 0.02). TAC patients showed significantly higher "regulatory" DC2:DC1 ratios (10 +/- 7.6) compared with non-TAC patients (4.1 +/- 2.3) (p = 0.04). Although sHLA-G levels appeared higher in TAC patients, the differences were not statistically significant. In conclusion, IS monotherapy provides an opportunity to investigate regulatory roles of individual agents. SRL maintenance and prior AL induction in subsets of patients appeared to show a regulatory T cell immunophenotype. However, TAC patients may have other regulatory characteristics, supporting the need for larger, prospective studies to clarify differences.

Buruli ulcer: reductive evolution enhances pathogenicity of Mycobacterium ulcerans

Buruli ulcer is an emerging human disease caused by infection with a slow-growing pathogen, Mycobacterium ulcerans, that produces mycolactone, a cytotoxin with immunomodulatory properties. The disease is associated with wetlands in certain tropical countries, and evidence for a role of insects in transmission of this pathogen is growing. Comparative genomic analysis has revealed that M. ulcerans arose from Mycobacterium marinum, a ubiquitous fast-growing aquatic species, by horizontal transfer of a virulence plasmid that carries a cluster of genes for mycolactone production, followed by reductive evolution. Here, the ecology, microbiology, evolutionary genomics and immunopathology of Buruli ulcer are reviewed.

The PI3K/Akt/mTOR pathway in innate immune cells: emerging therapeutic applications

The phosphatidylinositol-3 kinases (PI3Ks) and the mammalian target of rapamycin (mTOR) pathway have long been recognised as critically regulating metabolism, growth or survival. Recent data indicate that these molecules are also integral players in coordinating defence mechanisms in the innate immune system. In this respect, PI3K and mTOR positively regulate immune cell activation in neutrophils and mast cells. In plasmacytoid dendritic cells, these pathways have recently emerged as important regulators for type I interferon production via activation of the interferon-regulatory factor 7. Interestingly, in myeloid immune cells, PI3K and mTOR seem to constrain full immune cell activation by upregulation of the key anti-inflammatory cytokine interleukin 10 and inhibition of proinflammatory cytokines. These new insights into innate immune cell regulation may pave the way for manipulating distinct features of the innate immune system for therapeutic treatment of various inflammatory diseases and for implementation of improved vaccination strategies.

Salmonella osteomyelitis in an immunocompromized patient presenting as a primary lymphoma of the bone

During the past few decades, an increasing number of immunosuppressive drugs have been developed to treat autoimmune and rheumatic diseases, as well as post-transplant patients. In parallel, the incidence of immunocompromized patients in the general population has risen, for example, patients who are HIV positive, undergoing hemodialysis or suffering from diabetes mellitus. In such predisposed patients, infections with organisms of even reduced invasive potential can result in atypical invasive manifestations. In industrialized countries, an increase in the number of human non-typhoid Salmonella infections was observed in the 1980-1990s [Shimoni Z, Pitlik S, Leibovici L, Samra Z, Konigsberger H, Drucker M, et al. Nontyphoid Salmonella bacteremia: age-related differences in clinical presentation, bacteriology, and outcome. Clin Infect Dis 1999;28:822-7]. Beyond the main clinical manifestation of gastroenteritis, there is an increasing prevalence of extra-intestinal infections by this pathogen. We report a patient with acute osteomyelitis due to Salmonella typhimurium without any previous signs of gastroenteritis.

Effect of Skin Sensitizers on Inducible Nitric Oxide Synthase Expression and Nitric Oxide Production in Skin Dendritic Cells: Role of Different Immunosuppressive Drugs

Nitric oxide (NO) is involved in the pathogenesis of acute and chronic inflammatory conditions, namely in allergic contact dermatitis (ACD). However, the mechanism by which NO acts in ACD remains elusive. The present study focuses on the effects of different contact sensitizers (2,4-dinitrofluorbenzene, 1,4-phenylenediamine, nickel sulfate), the inactive analogue of DNFB, 2,4-dichloronitrobenzene, and two irritants (sodium dodecyl sulphate and benzalkonium chloride) on the expression of the inducible isoform of nitric oxide synthase (iNOS) and NO production in skin dendritic cells. It was also studied the role of different immunosuppressive drugs on iNOS expression and NO production. Only nickel sulfate increased the expression of iNOS and NO production being these effects inhibited by dexamathasone. In contrast, cyclosporin A and sirolimus, two other immunosuppressive drugs tested, did not affect iNOS expression triggered by nickel.

Nuclear receptor signalling in dendritic cells connects lipids, the genome and immune function

Dendritic cells (DCs) are sentinels of the immune system and represent a heterogeneous cell population. The existence of distinct DC subsets is due to their inherent plasticity and to the changing microenvironment modulating their immunological properties. Numerous signalling pathways have impacts on DCs. It appears that besides cytokines/chemokines, lipid mediators also have profound effects on the immunogenicity of DCs. Some of these lipid mediators exert an effect through nuclear hormone receptors. Interestingly, more recent findings suggest that DCs are able to convert precursors to active hormones, ligands for nuclear receptors. Some of these DC-derived lipids, in particular retinoic acid (RA), have a central function in shaping T-cell development and effector functions. In this review, we summarize and highlight the function of a set of nuclear receptors (PPARγ, RA receptor, vitamin D receptor and glucocorticoid receptor) in DC biology. Defining the contribution of nuclear hormone receptor signalling in DCs can help one to understand the regulatory logic of lipid signalling and allow the exploitation of their potential for therapeutic intervention in various immunological diseases.

Mechanisms of disease: the evolving understanding of liver allograft rejection

Liver transplantation is a successful treatment for select forms of liver disease and is unrivalled amongst other forms of solid organ transplantation in the ability of the recipient to develop long-term tolerance to the allograft. Much of this success can be attributed to the inherently tolerogenic manner in which antigens are presented in the liver and the presence of specialized regulatory lymphocyte populations. These observations are not universal, however, and a proportion of recipients develop problematic allograft rejection. Anti-allograft responses lead to an influx of effector cells that target hepatic parenchymal cells and induce apoptosis through members of the tumor necrosis factor superfamily. Anti-rejection therapies have traditionally targeted the entire lymphocyte response against the allograft and, whilst these therapies have been efficacious at limiting effector cell responses, they have also had deleterious effects on the regulatory cell populations that are required to promote long-term tolerance. The emergence of newer anti-rejection drugs that have the potential to target the effector response selectively, whilst preserving the much needed tolerogenic responses, has afforded us the opportunity to refine our future immunosuppressant strategies.

Corticosterone impairs dendritic cell maturation and function

Dendritic cells (DC) play a critical role in initiating and directing adaptive immune responses against pathogens and tumours. Immature DC are thought to act as sentinels in peripheral tissues where their main function is to capture antigen at sites of infection, whereas mature DC are highly efficient at priming T-cell-mediated immune responses against infectious pathogens. The DC maturation process is thought to be an important step in the efficient generation of cytotoxic T lymphocytes (CTL). It is well established that many aspects of immune function, including CTL-mediated antiviral immunity, are modulated by neuroendocrine-derived products. Corticosterone (CORT), an adrenal hormone produced at increased concentrations during a stress response, has been shown to play a role in impaired CTL responses in stressed animals, leading to high mortality in mice normally resistant to viral infection. While direct effects of neuroendocrine mediators on CTL have been studied, little is known about their effects on DC that are critical for CTL priming. Here, we found that physiologically relevant concentrations of CORT, acting via the glucocorticoid receptor, functionally compromise DC maturation. DC exposed to CORT remained phenotypically and functionally immature after stimulation with lipopolysaccharide and were impaired for the production of interleukin (IL)-6, IL-12, and tumour necrosis factor-alpha. These effects were biologically significant, as CORT treatment resulted in a marked reduction in the ability of DC to prime naive CD8(+) T cells in vivo. These findings offer a potential mechanism underlying stress-associated immunosuppression.

Shared signaling networks active in B cells isolated from genetically distinct mouse models of lupus

Though B cells play key roles in lupus pathogenesis, the molecular circuitry and its dysregulation in these cells as disease evolves remain poorly understood. To address this, a comprehensive scan of multiple signaling axes using multiplexed Western blotting was undertaken in several different murine lupus strains. PI3K/AKT/mTOR (mTOR, mammalian target of rapamycin), MEK1/Erk1/2, p38, NF-kappaB, multiple Bcl-2 family members, and cell-cycle molecules were observed to be hyperexpressed in lupus B cells in an age-dependent and lupus susceptibility gene-dose-dependent manner. Therapeutic targeting of the AKT/mTOR axis using a rapamycin (sirolimus) derivative ameliorated the serological, cellular, and pathological phenotypes associated with lupus. Surprisingly, the targeting of this axis was associated with the crippling of several other signaling axes. These studies reveal that lupus pathogenesis is contingent upon the activation of an elaborate network of signaling cascades that is shared among genetically distinct mouse models and raise hope that targeting pivotal nodes in these networks may offer therapeutic benefit.

Inhibition of endogenous MHC class II-restricted antigen presentation by tacrolimus (FK506) via FKBP51

The effect of tacrolimus (FK506) on down-regulation of IL-2 production by T cells is considered to be mainly responsible for its strong suppression of immunological events. In this study, we show that FK506 also has an affect on antigen presentation by antigen-presenting cells in vitro. FK506 was able to inhibit the presentation of endogenous MHC class II-restricted minor histocompatibility antigens in primary dendritic cells (DC) in vitro, but cyclosporine A (CsA) and rapamycin (RAP) were not. RNA interference (RNAi)-mediated reduction of endogenous FK506-binding protein (FKBP)51 expression resulted in a marked decrease in antigen presentation, suggesting that FKBP51 plays a role in endogenous MHC class II-restricted antigen presentation. Since our model used naturally expressed cytosolic antigens in primary DC, these effects might have been due to novel properties of the immunosuppressive drugs and may allow us to elucidate a new paradigm for the immunosuppressive mechanism of FK506.

Selective suppression of dendritic cell functions by Mycobacterium ulcerans toxin mycolactone

Mycolactone is a polyketide toxin produced by Mycobacterium ulcerans (Mu), the causative agent of the skin disease Buruli ulcer (BU). Surprisingly, infected tissues lack inflammatory infiltrates. Structural similarities between mycolactone and immunosuppressive agents led us to investigate the immunomodulatory properties of mycolactone on dendritic cells (DCs), the key initiators and regulators of immune responses. At noncytotoxic concentrations, phenotypic and functional maturation of both mouse and human DCs was inhibited by mycolactone. Notably, mycolactone blocked the emigration of mouse-skin DCs to draining lymph nodes, as well as their maturation in vivo. In human peripheral blood–derived DCs, mycolactone inhibited the ability to activate allogeneic T cell priming and to produce inflammatory molecules. Interestingly, production of the cytokines interleukin (IL) 12, tumor necrosis factor α, and IL-6 was only marginally affected, whereas production of the chemokines macrophage inflammatory protein (MIP) 1α, MIP-1β, regulated on activation, normal T cell expressed and secreted, interferon γ–inducible protein 10, and monocyte chemoattractant protein 1 was abolished at nanomolar concentrations. Importantly, mycolactone endogenously expressed by Mu mediated similar inhibitory effects on β-chemokine production by DCs. In accordance with the histopathological features of BUs, our results suggest that bacterial production of mycolactone may limit both the initiation of primary immune responses and the recruitment of inflammatory cells to the infection site. Moreover, they highlight a potential interest in mycolactone as a novel immunosuppressive agent.

Neuroendocrine regulation of skin dendritic cells

It has long been postulated that stress can affect certain skin conditions, and there is increasing experimental evidence that the neuroendocrine system can directly participate in cutaneous inflammation. Neurohormones, such as glucocorticoids and catecholamines, can reach the skin through the bloodstream after activation of the hypothalamic-pituitary-adrenal axis and the sympathetic nervous system, respectively. Multiple neuropeptides, among them calcitonin gene-related peptide, alpha-melanocyte stimulating hormone, pituitary adenylate cyclase-activating peptide, substance P, vasoactive intestinal peptide, and norepinephrine, may be released by cutaneous nerves or resident and infiltrating cells within the skin. Systemic neuromediators and cutaneous nerves can influence a number of target cells within the skin, among them Langerhans cells. Most of the experimental evidence to date indicates a suppressive effect of the neurohormones and neuropeptides on Langerhans cell function and cutaneous inflammation, but it has become evident lately that the timing of exposure to a stimulus is critical to the outcome of the immune response. Thus, administration of a stress hormone or exposure to a stressor before the dendritic cell (DC) encounters an antigen (Ag) may diminish the immune response toward that Ag, while a stressor may enhance immune function when acting on a maturing DC or before reexposure to the Ag. The neuroendocrine regulation of skin DCs is a complex system allowing for a quick adaptation to various stressors. Such a system, originally evolved to defend the organism against invading pathogens and maintain homeostasis, may under certain conditions become unbalanced and ultimately exacerbate cutaneous inflammation.

Effect of pentoxifylline on differentiation and maturation of human monocyte-derived dendritic cells in vitro

Pentoxifylline (PTX) is a drug used for the treatment of vascular disorders, but it also has a positive therapeutic effect in experimental models of some autoimmune diseases. In this work, we studied the effect of PTX on human monocyte-derived dendritic cells (MDDCs). Immature MDDCs were generated in vitro from monocytes in the presence of recombinant human granulocyte macrophage-colony stimulating factor (rhGM-CSF) and recombinant human interleukin-4 (rhIL-4), while mature MDDCs were obtained by cultivation of immature MDDCs with lipopolysaccharide (LPS). PTX (200 micro g/ml) was added at the beginning of cell cultivation. We found that PTX significantly impaired differentiation and function of immature MDDCs, as judged by the reduced allostimulatory activity of these cells on allogeneic T cells and down-regulation of costimulatory and adhesion molecules, such as CD86, CD40 and CD54. The maturation of MDDCs in the presence of PTX and LPS was characterized by the decreased expression of maturation marker CD83 and costimulatory molecule CD86, as well as lower stimulation of alloreactive T cells compared to the control MDDCs cultivated with LPS alone. PTX-treated MDDCs which were induced to mature with LPS produced lower levels of TNF-alpha, IL-12 and IL-18 and higher levels of IL-10 than corresponding control MDDCs. PTX did not significantly alter endocytosis of dextran by both immature and mature MDDCs. Cumulatively, our results show for the first time that PTX might impair differentiation, maturation and function of human MDDCs in vitro, suggesting an additional mechanism of its immunomodulatory activity.

Superior Immunomodulatory Effects of Intravenous Immunoglobulins on Human T-cells and Dendritic Cells: Comparison to Calcineurin Inhibitors

BACKGROUND

Prophylactic administration of anti-HBs intravenous immunoglobulins (IVIg) in hepatitis B infected-liver transplant patients protects against acute rejection. To explore the suitability of intravenous immunoglobulins (IVIg) as prophylaxis of acute rejection and graft-versus-host disease (GVHD) after allograft transplantation, the effects of IVIg and calcineurin inhibitors (CNI) on human blood-derived T-cells and DC were compared.

METHODS

T-cells were stimulated with phytohemagglutinin (PHA) or allogeneic spleen antigen-presenting cells (APC) and T-cell proliferation and cytokine production were determined in presence or absence of IVIg or CNI. Immature blood dendritic cells (DC) were stimulated in presence or absence of IVIg or CNI, and allogeneic T-cell stimulatory capacity, cell death, and phenotypic maturation were established.

RESULTS

IVIg and CNI equally inhibited T-cell proliferation and IFN-gamma production after PHA stimulation or allogeneic stimulation. CD8+ T-cells were preferentially affected by both IVIg and CNI after allogeneic stimulation. Like CNI, addition of IVIg at later time points after T-cell activation suppressed mitotic progression of responding T-cells. IVIg-treated DC were suppressed in their capacity to stimulate allogeneic T-cell proliferation by 73+/-12%, whereas DC-function was not affected by CNI. The decreased allogeneic T-cell stimulatory capacity of IVIg-treated DC correlated to induction of cell death in DC and decreased up-regulation of CD40 and CD80.

CONCLUSIONS

In vitro IVIg functionally inhibit the two principal immune cell-types involved in rejection and GVHD, i.e. T-cells and DC, whereas CNI only suppress T-cells. By targeting both T-cells and DC, IVIg may be a promising candidate for immunosuppressive treatment after allograft transplantation.

Ethanol affects the generation, cosignaling molecule expression, and function of plasmacytoid and myeloid dendritic cell subsets in vitro and in vivo

The influence of ethanol (EtOH) on multiple dendritic cell (DC) subsets, in the steady state or following their mobilization in vivo, has not been characterized. Herein, generation of mouse bone marrow-derived DC (BMDC) in response to fms-like tyrosine kinase 3 ligand was inhibited by physiologically relevant concentrations of EtOH with selective suppression of plasmacytoid (p)DC. EtOH reduced surface expression of costimulatory molecules (CD40, CD80, CD86) but not that of coinhibitory CD274 (B7-H1) on resting or CpG-stimulated DC subsets. Interleukin (IL)-12p70 production by activated DC was impaired. Consistent with these findings, EtOH-exposed BMDC exhibited a reduced capacity to induce naïve, allogeneic T cell proliferation and impaired ability to prime T cells in vivo. DC subsets freshly isolated from EtOH-fed mice were also examined. Liver DC, inherently immature and resistant to maturation, exhibited little change in their low surface cosignaling molecule expression, whereas splenic DC showed reduced expression of surface costimulatory molecules in response to CpG stimulation in vivo. These splenic DC elicited reduced naïve, allogeneic T cell proliferation in vitro, and the stimulatory capacity of resting but not CpG-activated liver DC was reduced by chronic EtOH administration. T cells from animals primed with EtOH-exposed DC produced elevated levels of IL-10 following ex vivo challenge with donor alloantigen. Thus, EtOH impairs cytokine-driven differentiation and function of myeloid DC and pDC in vitro. Hepatic DC from chronic EtOH-fed mice are less affected than splenic DC, which exhibit impaired functional maturation following CpG stimulation. These results indicate a potential mechanism by which alcohol consumption is associated with immunosuppression.

Dexamethasone preferentially suppresses plasmacytoid dendritic cell differentiation and enhances their apoptotic death

Plasmacytoid dendritic cells (pDC) are an important source of type-1 interferon (IFN) following microbial infection and also play key roles in the induction of innate and adaptive immune responses. Here, we show that the glucocorticoid (GC) dexamethasone (Dex) strikingly reduces pDC (and myeloid DC) numbers in secondary lymphoid tissue and liver of normal and hematopoietic growth factor-mobilized mice and suppresses pDC differentiation from bone marrow precursors in vitro. Moreover, the apoptotic death of pDC in vitro was enhanced by exposure to Dex. Notably, however, Toll-like receptor 9 expression and virally induced IFNalpha production by residual pDC from Dex-treated animals were unaffected. Thus, whereas marked reduction in absolute numbers of pDC by GC may predispose to viral infection, often associated with GC-mediated immunosuppression, reductions in pDC and IFNalpha production may contribute to the beneficial effects on GC observed in systemic autoimmune disease, in which that both pDC and IFNalpha have been implicated.

Chronic Graft-Versus-Host Disease

Chronic graft-versus-host disease (cGVHD) is the most common and severe complication among patients surviving >100 days after allogeneic transplantation. It starts with the expansion of donor T cells in response to alloantigens or autoantigens that are unchecked by normal thymic or peripheral mechanisms of deletion. The T cells induce damage to target organs either directly through cytolytic attack, inflammatory cytokines and fibrosis, or by promoting B cell activation and production of autoantibodies. HLA disparity, donor and patient age and sex, source of progenitor cells, graft composition and previous acute GVHD are the main factors that predict the risk of developing cGVHD. Once the diagnosis has been established, patients needing treatment (extensive cGVHD) must be identified. Poor prognostic factors such as extensive skin involvement, thrombocytopenia and progressive-type onset of cGVHD must be considered in order to define the immunosuppressive treatment requirements. Prednisone, together with a calcineurin inhibitor such as ciclosporin or tacrolimus, can be considered the standard regimen as primary treatment for cGVHD. Using that approach, among high-risk patients (identified as those with extensive cGVHD plus thrombocytopenia) 3-year survival reached 52%. Concerning salvage regimens, to date there is no clear standard regimen for cGVHD treatment, the best choice being to enter the patient into a clinical trial. Immunosuppressive drugs that inhibit T cell activation, proliferation or survival, such as mycophenolate mofetil, the anti-interleukin-2 alpha receptor antagonist daclizumab, sirolimus (rapamycin), extracorporeal photopheresis and pentostatin (deoxycoformycin), among other agents, have been used with a very wide range of complete responses ranging from 5% to 50%. In addition, anti-cytokine or B cell inhibitors such as etanercept or rituximab have also been evaluated. The severe immunosuppression induced by those drugs increases the risk of infectious complications and may have a deleterious effect on the graft versus tumour effect after transplant so that newer strategies based on the selective depletion of alloreactive T cells and induction of more specific immunotolerance against host tissues are required.

Therapeutic potential of target of rapamycin inhibitors

Target of rapamycin (TOR) functions within the cell as a transducer of information from various sources, including growth factors, energy sensors, and hypoxia sensors, as well as components of the cell regulating growth and division. Blocking TOR function mimics amino acid, and to some extent, growth factor deprivation and has a cytostatic effect on proliferating cells in vivo. Inhibition of TOR in vivo, utilising its namesake rapamycin, leads to immunosuppression. This property has been exploited successfully with the use of rapamycin and its derivatives as a therapeutic agent in the prevention of organ rejection after transplantation with relatively mild side effects when compared to other immunosuppressive agents. The cytostatic effect of TOR on vascular smooth muscle cell proliferation has also recently been exploited in the therapeutic application of rapamycin to drug eluting stents for angioplasty. These stents significantly reduce the amount of arterial reblockage that results from proliferating vascular smooth muscle cells. In cancer, the effect of blocking TOR function on tumour growth and disease progression is currently of major interest and is the basis for a number of ongoing clinical trials. However, different cell types and tumours respond differently to TOR inhibition, and TOR is clearly not cytostatic for all types of cancer cells in vitro or in vivo. As the molecular details of how TOR functions and the targets of TOR activity are further elucidated, tumour and tissue specific functions are being identified that implicate TOR in angiogenesis, apoptosis, and the reversal of some forms of cellular transformation. This review will describe our current understanding of TOR function, describe the current strategies for employing TOR inhibitors in clinical and preclinical development, and outline future strategies for appropriate targets of TOR inhibitors in the treatment of disease.

Dexamethasone Induces IL-10-Producing Monocyte-Derived Dendritic Cells with Durable Immaturity

It is highly desirable that immature dendritic cells (DC) used for tolerance induction maintain steady immature state with predominant interleukin (IL)-10 production. In this study, we attempted to develop DC with durable immaturity and other tolerogenic features by using dexamethasone (Dex). We found DC derived from human monocytes in the presence of 10(-7) m Dex were negative for CD1a. Compared with control transduced DC (Ctrl-DC), Dex-DC expressed lower CD40, CD80 and CD86 but equivalent human leucocyte antigen-DR. Both immature Dex- and Ctrl-DC did not express CD83. Nevertheless, upon stimulation of lipopolysaccharide (LPS) or CD40 ligand, the expression of CD40, CD80, CD83 and CD86 was upregulated on Ctrl-DC but not on Dex-DC. The immaturity of Dex-DC was durable following Dex removal. Interestingly, Dex-DC maintained production of large amount of IL-10 and little IL-12 five days after Dex removed. Further study indicated that high-level IL-10 production by Dex-DC was associated with high-level phosphorylation of extracellular signal-regulated kinase (ERK) as blockade of this enzyme markedly attenuated IL-10 production. Furthermore, Dex-DC sustained the capability of high phosphorylation of ERK and IL-10 production 5 days after Dex removal. In addition, Dex-DC had significantly lower activity in stimulating T-cell proliferation. Neutralization of IL-10, to some extent, promoted DC maturation activated by LPS, as well as T-cell stimulatory activity of Dex-DC. The above findings suggest that IL-10-producing Dex-DC with durable immaturity are potentially useful for induction of immune tolerance.

Induction of leukemia-specific CD8+ cytotoxic T cells with autologous myeloid leukemic cells maturated with a fiber-modified adenovirus encoding TNF-alpha

Acute myeloid leukemia (AML) cells can be differentiated into dendritic cells (DCs) using appropriate combinations of cytokines but generation of autologous antileukemic cytotoxic T cells using leukemic DCs remains difficult. Transduction by adenoviral vectors has been reported to induce efficient maturation of monocyte-derived DCs but AML cells are generally resistant to adenoviral gene transfer. In this study we tested the effects of adenoviral TNF-alpha gene transfer on maturation of AML cells using the fiber-modified AdTNF.F(pK7) adenovirus. All samples expressed high and sustained levels of TNF-alpha following transduction. AdTNF.F(pK7) induced significantly greater maturation of AML cells into antigen-presenting cells (APC) than did recombinant TNF-alpha or control adenoviral vector. Maturation of leukemic cells into APCs was mediated at least partially via a PI3K/mTOR pathway, as the inhibitors LY294002, wortmannin, and rapamycin inhibited the maturation effect induced by the AdTNF.F(pK7) adenovirus. In addition, CD8+ T cells expanded with AdTNF.F(pK7)-transduced AML cells showed greater expansion and specific CD8+ CTL activity against autologous AML cells than T cells expanded by other means. Thus, fiber-modified adenoviral vectors encoding TNF-alpha are able to maturate AML cells into APCs with high efficacy and reproducibility, providing a useful tool to generate efficiently specific CD8+ CTLs against leukemic disease.

Immune responses to gene therapy vectors: influence on vector function and effector mechanisms

Circumventing the immune response to the vector is a major challenge with all vector types. Viral vectors are the most likely to induce an immune response, especially those, like adenovirus and AAV, which express immunogenic epitopes within the organism. The first immune response occurring after vector transfer emerges from the innate immune system, mainly consisting in a rapid (few hours) inflammatory cytokines and chemokines secretion around the administration site. This reaction is high with adenoviral vectors and almost null with AAV. It is noteworthy that plasmid DNA vectors, because of CpG stimulatory islets, also stimulate the innate immunity via the stimulation of TLR receptors on leukocytes. Specific immune response leading to antibodies production and T lymphocytes activation also occurs within a few days after vector introduction. Capsid antigens are mostly responsible for specific immunity toward adenoviruses, and are also involved in the response against AAV. In the former case only, however, viral gene-encoded proteins can also be immunogenic. The pre-existing humoral immunity coming from early infections with wild-type AAV or adenovirus can prevent efficient gene transfer with the corresponding vectors. In all cases, some parameters like route of administration, dose, or promoter type have been extensively described as critical factors influencing vector immunity. Strategies to fight against vector-induced immunity can come from the immunology field, since tolerance induction or immunosuppression are a possibility. Alterations to vector structure have also been extensively performed to circumvent the immune system and thus enhance gene transfer efficiency and safety.

Both T and non-T cells with proliferating potentials are effective in inducing suppression of allograft responses by alloantigen-specific intravenous presensitization combined with suboptimal doses of 15-deoxyspergualin

In an MHC class I-disparate combination of mouse strains, a single intravenous injection of donor spleen cells combined with 10 suboptimal doses of 15-deoxyspergualin (DSG) administration was effective in inducing donor-specific suppression of cytotoxic T-lymphocyte (CTL) responses and prolonged survival of the relevant skin allograft. Proliferative potentials of the donor spleen cells were requirement for the induction of suppressed allospecific responses, but both highly purified T cells and non-T cells were equally effective to induce the suppression of CTL responses by intravenous injection. These results have shown that, although working on different mechanisms, DSG is as effective as FK506 or rapamycin in inducing allograft tolerance when used at suboptimal doses along with the donor-specific intravenous presensitization, and an immune mechanism other than well-characterized veto T cells is working in this model in suppressing alloreactive CTL precursors.

T-cell anergy

Self-reactive T cells that escape negative selection in the thymus must be inactivated in the periphery. Anergy constitutes one means of imposing peripheral tolerance. Anergic T cells are functionally inactivated and unable to initiate a productive response even when antigen is encountered in the presence of full co-stimulation. Recent studies have provided new insights into the mechanisms responsible for the induction and maintenance of T-cell anergy. These studies have helped clarify the nature of the signals that induce tolerance, the cells able to deliver them and the molecular processes that underlie the unresponsive state.